Pupil sheet · Giant structures
A sea of electrons — questions
Name ______________________ Date ____________
Try every question before you use a nudge. Write in full sentences where you are asked to explain.
1. describe
Which statement describes metallic bonding?
Circle one answer.
- Positive ions attracted to negative ions between them
- Positive ions attracted to a sea of delocalised electrons
- Pairs of electrons shared between two neighbouring atoms
- Weak forces that hold layers of metal atoms together
Nudge (only if you are stuck): Think about what a metal atom does with its outer electrons, and what charge it is left with.
2. give
A pupil wrote four sentences about the bonding in potassium, a Group I metal. Each sentence has one wrong word, in capitals. Give the correct word for each sentence.
1. “Each potassium atom GAINS its one outer electron.”
2. “So each atom becomes a NEGATIVE ion.”
3. “The ions are held together in a giant MOLECULAR lattice.”
4. “The lattice holds together because of the electrostatic REPULSION between the ions and the sea of electrons they lost.”
Nudge (only if you are stuck): For each sentence, ask: which way do the electrons go, what charge does each particle have, and does a metal contain separate molecules?
3. identify
Four solids are described below by their particles. Identify the solid that conducts electricity.
Circle one answer.
- Atoms whose outer electrons are all used in covalent bonds
- Positive ions surrounded by a sea of delocalised electrons
- Positive and negative ions held in fixed places in a lattice
- Small molecules whose electrons stay inside each molecule
Nudge (only if you are stuck): A current is a flow of charge. What must a solid contain, and what must those particles be able to do?
4. identify
A farrier heats an iron bar until it glows and hammers it into a horseshoe. The glowing iron is still far below its melting point of about 1540 °C, and it changes shape without cracking. Which row names this property of iron and explains it?
| Row | Property | What happens to the particles when the iron is hammered |
|---|---|---|
| A | ductile | the layers of positive ions slide over each other, and the sea of delocalised electrons still attracts them in their new places |
| B | malleable | the metallic bonding is weak, so the ions flow past each other like a liquid |
| C | ductile | the metallic bonding is weak, so the ions flow past each other like a liquid |
| D | malleable | the layers of positive ions slide over each other, and the sea of delocalised electrons still attracts them in their new places |
Circle one answer.
- A
- B
- C
- D
Nudge (only if you are stuck): Take one column at a time: first the name of the property, then what happens to the particles.
5. deduce
Solid X conducts electricity as a solid and when molten, and it can be drawn out into a thin wire without breaking. Deduce which statement about the structure of X must be true.
Circle one answer.
- Positive and negative ions that are free to move when molten
- Small molecules held to each other only by weak forces
- Layers of atoms held to each other only by weak forces
- Positive ions in layers, in a sea of delocalised electrons
Nudge (only if you are stuck): Use both clues. Which kinds of solid conduct even when solid? Which of those can be pulled out in one piece?
6. explain
A strip of tin can be bent without breaking. A thin wafer of silicon, which has a giant covalent structure like diamond, snaps when it is bent. (a) Explain, in terms of structure and bonding, why tin bends without breaking. (b) Explain why the silicon snaps.
(a) Why tin bends without breaking
(b) Why silicon snaps
Nudge (only if you are stuck): Tin: what attracts the ions, and does that change when they move? Silicon: what holds each atom to its neighbours, and what happens to that if the atoms move?
7. deduce / calculate
In a metal, each atom gives its outer electrons to the sea of delocalised electrons. (a) Lithium is in Group I. Deduce the number of delocalised electrons that each lithium atom gives. (b) Calcium is in Group II. Deduce the number that each calcium atom gives. (c) A tiny model piece of calcium has 400 calcium ions. Calculate the number of delocalised electrons in its sea.
(a) Electrons from each lithium atom: ______________ unit ________
(b) Electrons from each calcium atom: ______________ unit ________
(c) Delocalised electrons in the sea: ______________ unit ________
Nudge (only if you are stuck): The Group number gives the number of outer electrons.
8. identify
In an electrolysis cell, copper wires carry the current to graphite electrodes dipped in molten sodium chloride. Which row shows the particles that carry the current in each?
| Row | Copper wire | Graphite electrode | Molten sodium chloride |
|---|---|---|---|
| A | delocalised electrons | ions | ions |
| B | positive ions | delocalised electrons | delocalised electrons |
| C | delocalised electrons | delocalised electrons | ions |
| D | delocalised electrons | delocalised electrons | delocalised electrons |
Circle one answer.
- A
- B
- C
- D
Nudge (only if you are stuck): For each one, ask: does it contain ions, delocalised electrons, or both? Which of them can move?
9. deduce / explain
(a) A model piece of a metal M has 300 positive ions and 600 delocalised electrons, and it has no overall charge. Deduce the charge on each ion of M, and the group of the Periodic Table that M is in. (b) Lead, a metal, and graphite both have layers that can slide over each other. Lead can be hammered into thin sheets for roofs, but graphite crumbles into flakes when it is hammered. Explain the difference.
(a) The charge on each ion, and the group of M
(b) Why lead flattens but graphite crumbles
Nudge (only if you are stuck): For (a), the metal has no overall charge. For (b), ask what holds the layers together after they slide, in each solid.